1. Field of the Invention
The present general inventive concept relates to a light guide panel usable with a backlight unit, a backlight unit employing the same, and a manufacturing method thereof, and more particularly, to a light guide panel usable with a backlight unit and a manufacturing method thereof, which can improve brightness uniformity, enhance light utilization by preventing light loss, reduce manufacturing costs, and simplify a manufacturing process.
2. Description of the Related Art
A backlight unit is disposed at a rear side of a liquid crystal display (LCD) panel and is used to convert a line light source into a uniform surface light source and to illuminate a liquid crystal display (LCD) panel. Initially, backlight units had several lamps arranged at a rear side of an LCD panel at constant intervals. Recently, an edge light type backlight unit has been widely used because it is advantageous to the slimness and the lifetime of the LCD.
FIG. 1 is an exploded side sectional view of a conventional backlight unit.
Referring to FIG. 1, a conventional backlight unit includes a lamp 10, a lamp reflector 11, a reflect panel 30, a light guide panel 20, a diffuse panel 40, a brightness enhancement film 50, and a polarization enhancement film 60.
The lamp 10 is a line light source for the backlight unit. The lamp reflector 11 reflects a light, which is radiated from the lamp 10 in a direction opposite to the light guide panel 20, so that the light can be propagated to the light guide panel 20. The light guide panel 20 receives the light of the one-dimensional line light source from the lamp 10 and the lamp reflector 11 through one side and converts the line light source into a surface light source. Light from the surface light source is propagated to the diffuse panel 40. The reflect panel 30 reflects light incident from the light guide panel 20, so that the light can be redirected to the light guide panel 20. The diffuse panel 40 scatters the light propagated from the light guide panel 20, such that the light is uniformly distributed. The brightness enhancement film 50 refracts and focuses the light propagated from the diffuse panel 40, such that straightness and brightness of the light is enhanced. The brightness enhancement film 60 enhances polarization efficiency of the light propagated from the brightness embodiment film 50 and thus improves light efficiency.
The light guide panel 20 is an essential part of the backlight unit. The conventional light guide panel 20 includes a light scatter layer, which is formed on a lower surface of a transparent acrylic resin plate. When line light source is irradiated to one side surface of the light guide panel 20, the irradiated light is totally reflected to the upper and lower surfaces of the light guide panel 20 and is vertically scattered by the light scatter layer, and then passes through the light guide panel 20.
Referring to FIG. 2, the light scatter layer is generally provided with dot light scatter patterns 21, which are arranged with different diameters, densities and pitches with respect to each other. In an example of FIG. 2, sizes of the dot light scatter patterns 21 increase depending on distance from the lamp 10. If the dot light scatter patterns 21 are formed with the same diameters, densities and pitches, positions near the lamp 10 are brighter than positions far from the lamp 10. Thus, brightness distribution of the light emitted from the light guide panel 20 becomes ununiform. In order to emit light with a uniform brightness distribution, the dot light scatter patterns 21 are formed with different diameters, densities and pitches, depending on their positions. A screen printing method is widely used to form the dot light scatter patterns 21.
As described above, when forming the light scatter layer of the light guide panel 20, the dot light scatter patterns 21 are modified so as to improve the brightness uniformity. That is, as the distance from the lamp 10 becomes greater, intensity of the light incident to the light guide panel 20 decreases. Also, the brightness of the light propagated along the light guide panel 20 and scattered at the dot light scatter patterns 21 is proportional to the areas of the dot light scatter patterns 21. Therefore, in order to obtain the uniform brightness distribution all over the light guide panel 20, the diameters of the dot light scatter patterns 21 are designed to increase according to a certain function as their distance from the line light source increases. Also, the pitches of the dot light scatter pattern 21 are designed to increase the uniformity by making the scattered light of the dot light scatter patterns 21 sufficiently overlap. The densities of the dot light scatter patterns 21 are also designed to increase uniformity. However, it is difficult to design the pattern arrangement with satisfactory brightness uniformity. It is usual that the satisfactory brightness uniformity may not be obtained even by several trials and errors.
Since the light is propagated through the total reflection until the light reaches the dot light scatter patterns 21, the light loss occurs as a moving path of the light becomes longer. Thus, only some of a total amount of the light emitted from the light source is propagated through the upper surface of the light guide panel 20, so that light utilization is degraded.
Further, when manufacturing the light guide panel 20, a process of printing the dot light scatter patterns 21 is not simple. One light guide panel includes thousands to tens of thousands of the dot light scatter patterns 21. The sizes of the dot light scatter patterns 21 range from tens of micrometers to thousands of micrometers. When forming small patterns, it is necessary to decrease viscosity of a print ink because the print ink is difficult to pass through a screen. In contrast, when forming large patterns, it is necessary to increase viscosity of the print ink because the print ink is easy to pass through the screen. Due to these conflicting requirement conditions, it is difficult to adjust the viscosity of the print ink. That is, when the viscosity is high, some of the dot patterns with small diameters may not be printed. When the viscosity is low, some of the dot patterns with large diameters may be spread out. Since it is difficult to properly adjust viscosity due to many dot patterns and their various sizes, process yield is degraded and therefore a manufacturing cost is increased.